This application relates to a heat-retaining sleeve for a fluorescent lamp for increasing the temperature of the ‘cold spot’ of the lamp to optimize the lumen output of the lamp.
All fluorescent lamps have an optimum temperature at which maximum lumen output is produced. The lumen output of fluorescent lamps is related to two characteristic temperatures: the ambient temperature, and the “cold spot” temperature. The ambient temperature is the temperature of the air immediately surrounding the lamp. The “cold spot” temperature is the temperature of the lamp itself at its coldest point, generally situated behind the electrode at the brand-stamp end of the lamp. Maximum lumen output is experienced when either the ambient temperature or the cold spot temperature reaches an optimum temperature. Certain linear fluorescent lamps, such as T-5 and T-5 HO lamps, operate at a relatively high optimum lighting temperature. (Hereafter, reference to a “T-5” lamp shall be understood to include a T-5 HO lamp) An ambient temperature of 35 degrees Celsius or a cold spot temperature of 43 to 46 degrees Celsius corresponds to conditions in the T-5 lamp which result in maximum lumen output.
Lamps in indirect lighting fixtures tend to operate at cooler temperatures than those in direct lighting fixtures. In the case of T-8 lamps, the operating temperature is near optimum. However, T-5 lamps in indirect lighting fixtures operate at a temperature which is cooler than the optimum and therefore do not produce maximum lumen output. Preliminary tests indicate that the lumen output of a T-5 lamp operating in an indirect lighting fixture is roughly ten percent lower than the optimum lumen output.
One attempt has been made to solve this problem by increasing the temperature of the cold spot of the lamp. Seeking to elevate the temperature of the lamp's cold spot, which is located at one end of the lamp, a cylindrical sleeve such as graphically illustrated in FIG. 1 has been devised to fit over that lamp end. As seen in FIG. 1, this sleeve includes an end portion having a reduced inner diameter that fits snugly onto the metal end cap of the lamp, and a relatively short extended portion that surrounds a short section of the lamp's glass envelope adjacent the lamp's cold spot to form a cylindrical air gap between the sleeve and lamp. This sleeve has proved to be ineffective. It conducts heat away from the lamp through the end cap and is too short to direct enough of the lamp's heat to the lamp's cold spot to appreciably elevate temperature. This type of sleeve has also proved to be difficult to install in an indirect lighting fixture due to crowding of the sleeve by the bottom reflector plate.
A need therefore exists for a solution that enables a linear fluorescent lamp, and particularly a T-5 lamp, in an indirect light fixture to operate at an optimum or near optimum temperature for increasing the lumen output of the lamp. A need also exists for a device that can be easily installed in indirect lighting fixtures for increasing the lumen output of the fluorescent lamps of T-5 fluorescent lighting fixtures.